The present invention relates generally to an improved pressure relief valve for fluid systems, and more particularly to a pressure relief valve which will typically respond to bypass a portion of the system capacity when system pressures become modestly in excess of normal working pressures, while continuing to maintain the system at approximately the desired operational pressures. The structure is also designed to provide fail-safe operation in the event of failure of the spring member which controls the pressure at which the valve will commence bypass. The pressure relief valve of the present invention has particular utility in applications where several terminal nozzles are employed using random off-and-on conditions, with a single pressure source, thereby achieving anywhere from partial to complete bypass of fluid while maintaining a predetermined working pressure within the system.
Typically, pressure relief or bypass valves have been designed to achieve an objective which is to function in response to system pressures which are equal to or greater than normal design working pressures. However, pressure relief or bypass valves have normally been designed to respond only when working pressures are substantially in excess of design pressures, thereby permitting at least temporary overload to occur in the system. For example, pressure relief or bypass valves may normally function only upon occurrence of dangerous pressure surges. Even temporary overload or surge may, in certain instances, damage system components, particularly system seals, pump piston cups, or other of the less durable components present in most fluid or hydraulic systems. The pressure relief valve of the present invention is arranged to respond to pressures which are only in modest excess of the working pressures and to continue to maintain the design working pressure, thereby providing greater control over the conditions present in the system.
The improved pressure relief valve of the present invention is particularly designed for systems which have widely variable demands. Such systems are frequently encountered in pressure washer systems utilizing a single pressure source, with a variety of outlet nozzles which function either intermittently or randomly. Typically, one pressure source may be utilized to provide fluid pressure for several working stations, with the individual demand requirements for each station being determined by the nature of the working situation. For example, in a car wash installation, several stations may be serviced by the same pump, with the flow of automobiles through the system being both intermittent and random.
Operation of the pressure relief valve of the present invention is achieved through bypass of a selected quantity of fluid from the system through a bypass orifice. The bypass orifice is designed to have a size such that the pressure drop of the fluid passing through the orifice is equal to a reasonably small fraction of the total working pressure, such as, for example, 10% of the normal working pressure. Under these conditions, substantially normal working pressure is always maintained at the inlet to the pressure relief valve and to other portions of the system. As such, the system may be designed to bypass fluid when only 70% of the system is calling for fluid under pressure, with the balance in a no-demand situation.